Polysulfone and poly(N-vinyl lactam) polymer alloy and fiber and filter materials made of the alloy

ABSTRACT

A polymer alloy has been developed comprising a polysulfone and a vinyl lactam polymer. The resulting alloy has excellent thermal characteristics and even in the presence of substantial quantities in vinyl lactam polymers, has solvent resistance to both organic and aqueous solvent materials. The materials, when dissolved in solvents, can be spun from a variety of solvents into a variety of useful fiber materials. The resulting fine fiber, microfiber and nanofiber materials have excellent thermal and chemical resistance for a variety of fiber applications. The polymer alloys of the invention can be spun into nanofiber mats that can act as a filtration media and can also be combined into conventional substrate materials for fabrication into filter structures.

FIELD OF THE INVENTION

The invention relates to polymer alloy material. Such a polymer alloyhas properties that can be used in making a fiber or fabricating afibrous structure. Such a fiber structure can be use in filtrationapplications due to environmental stability and filtration efficiency.The medium has high strength, efficiency, resistance to moisture andhigh capacity for filtration of particulate from a fluid (gas or liquid)stream. The filter medium or media comprise a non-woven web suitable forremoval of particulate from mobile fluids such as a gas, an aqueousstream or non-aqueous streams including air, waste gas, fuels,lubricating oils and hydraulic fluids. The invention relates tonon-woven media layers obtaining sufficient wet strength, particulateefficiency, permeability and other properties to survive the commonoperating conditions, such as variation in flow rate, temperature,pressure and particulate loading while removing substantial particulateloads from the fluid stream. Lastly, the invention relates to a methodof filtering gaseous and aqueous and non-aqueous liquids.

BACKGROUND OF THE INVENTION

The invention relates to a polymer alloy of a polysulfone and an N-vinyllactam polymer. The invention relates to fibers made from the alloy andapplications of the alloy fiber. One important application is in fibercontaining filter structures. Fine fiber materials are known in theprior art. We are aware of Barris et al., U.S. Pat. No. 4,650,506teaching a method of spinning fine fiber, Kahlbaugh et al., U.S. Pat.No. 5,672,399 teaching a filter structure comprising a separation mediaand a fine fiber layer in a multilayer structure, and a variety ofpatents on fine fiber media and filter structures, Chung et al., U.S.Pat. No. 6,743,273; Barris et al., U.S. Pat. No. 6,800,117; Gillinghamet al., U.S. Pat. No. 6,673,136; Gogins et al., U.S. Pat. No. 6,716,274;Buettner et al., U.S. Pat. No. 6,740,142; and Benson et al., U.S. Pat.No. 6,746,517.

The art has known for many years that the alloying of polymers to obtaina single glass transition temperature (Tg) material with a homogeneousmixture on a molecular level is difficult and rare. However, suchpolymer alloys can often obtain important novel properties that can betailored to specific end uses. Very often the properties of thehomogeneous alloy attains the best properties of its individualcomponents. The great majority of polymer mixtures fail to alloy, butforms a two-phase blend after mixing and the mixtures are oftencharacterized by reduced chemical, thermal, physical and structuralproperties and have two, three or more thermal transition or glasstransition temperatures. Further, alloys tend to be transparent and canbe processed as though they were single component thermoplastics. Whilegreat success has been obtained in the manufacture and use of fine fibermaterials in a variety of filtration applications, fine fiber materialscan be improved for excellent properties in gaseous or liquidfiltration. The materials are improved for use with high temperaturestability, and physical and mechanical stability in the presence oforganic or aqueous liquids while filtering liquid mobile fluids infiltration applications.

A substantial need exists in the art for such polymer materials in theform of an improved alloy that can be formed into improved nanofiber,microfiber and fine fiber structures. A further substantial need existsfor filtration media, filter structures and filtration methods that canbe used for removing particulate materials from fluid streams. Fluidsstreams include both gaseous and liquid streams. Typically gaseousfilters are filters for air or industrial waste gas streams. Liquidstreams or compositions include aqueous liquids and in particular,non-aqueous liquids such as fuels, lubricating oils and hydraulicfluids. The invention provides such media, filtration structures andmethods that are stable to the condition found in filtering gaseousstreams, air streams, aqueous and non-aqueous liquid streams. Thepolymer alloy fiber and provides a unique media or media layercombinations that achieve improved filtration properties includingsubstantial permeability, high wet strength, substantial efficiency andlong filtration life.

BRIEF DISCUSSION OF THE INVENTION

We have found a polymer alloy can be formed from a polysulfone and anN-vinyl lactam polymer (a poly(N-vinyl lactam)). The alloy comprises amaterial with a single phase, a single T_(g) and resistance to aqueousliquids, excellent thermal properties, chemical and solvent resistanceand the characteristic that it can be electrospun into nanofiber andmicrofiber.

The polymer fine fiber, with a diameter of 0.01 to 10 microns, 0.02 to 5microns or 0.03 to 1 micron, (microfiber and nanofiber) can be fashionedinto useful product formats (e.g., when formed onto a substrate). Thisfine fiber can be made in the form of an improved microfiltration mediastructure having layers of filtration materials. The fine fiber layersof the invention comprise a random distribution of fine fibers that canbe bonded to form an interlocking net.

Filtration performance is obtained largely as a result of the fine fiberbarrier to the passage of particulate. Structural properties ofstiffness, strength, pleatability are provided by the substrate to whichthe fine fiber adhered. The fine fiber interlocking networks have asimportant characteristics, fine fibers in the form of microfibers ornanofibers and relatively small openings, orifices, pores or spacesbetween the fibers. Such spaces or pore sizes typically range, betweenfibers, of about 0.01 to about 25 microns or often about 0.1 to about 10microns.

The filter products comprise a fine fiber layer formed on a substrate.Substrates can be made from fibers of synthetic, natural sources ormixed synthetic/natural materials. The fine fiber adds less than amicron in thickness to the overall fine fiber plus substrate filtermedia. In service, the filters can stop incident particulate frompassing through the fine fiber layer and can attain substantial surfaceloadings of trapped particles. The particles comprising dust or otherincident particulates rapidly form a dust cake on the fine fiber surfaceand maintain high initial and overall efficiency of particulate removal.

In general, the technology can be applied to filtering gaseous or liquidsystems. In liquid filtering techniques, the collection mechanism isbelieved to be sieving. In a single layer the efficiency is that of thelayer. The composite efficiency in a liquid application is limited bythe efficiency of the single layer with the highest efficiency. Theliquids would be directed through the media according to the invention,with particulates therein trapped in a sieving mechanism. In liquidfilter systems, i.e. wherein the particulate material to be filtered iscarried in a liquid, such applications include aqueous and non-aqueousand mixed aqueous/non-aqueous applications such as water streams, lubeoil, hydraulic fluid, fuel filter systems or mist collectors. Aqueousstreams include natural and man-made streams such as effluents, coolingwater, process water, etc. Non-aqueous streams include gasoline, dieselfuel, petroleum and synthetic lubricants, hydraulic fluid, brake fluidand other ester based working fluids, cutting oils, food grade oil, etc.Mixed streams include dispersions comprising water in oil and oil inwater compositions and aerosols comprising water and a non-aqueouscomponent. Other aqueous or mixed streams of relevance include fluids inthe biological, pharmaceutical, and food industries. These fluidsinclude those in the dairy product manufacturing, blood separations,virus and bacteria removal, etc.

BRIEF DISCUSSION OF THE DRAWINGS

FIGS. 1-3 are charts of differential scanning calorimetry studies of theindividual polymer components of the alloy (polyvinyl pyrrolidone andpolysulfone polymers) compared to the calorimetry of a alloy material.

FIGS. 4-20 are electron microscope SEM photo micrographs of a variety ofthe spun microfiber materials derived from the electrospinningexperiments from the experimental section.

FIG. 21 is a measure of the wetability or hydrophobicity of certain ofthe fibers from the experimental section showing that the alloy fibercontaining a substantial proportion of polyvinyl pyrrolidone issubstantially wetable and hydrophilic as measured by the contact anglemeasurement of the measuring procedure. Such a material can be used inaqueous filtration at low pressure drop and acceptable efficiency.

DETAILED DISCUSSION OF THE INVENTION

The invention relates to an improved alloy material, nanofiber andmicrofiber materials made from the improved alloy and to filtrationmaterials and methods including the fiber made from the alloy material.

The polymer materials as disclosed herein have substantially improvedresistance to the undesirable effects of heat, humidity, aqueousliquids, solvent streams, high flow rates, high particle loads, reversepulse cleaning, operational abrasion, submicron particulates, cleaningof filters in use and other demanding conditions in both gas and liquidfiltration. The improved microfiber and nanofiber performance is aresult of the improved character of the polymeric materials forming themicrofiber or nanofiber. Further, the filter media of the inventionusing the improved polymeric materials of the invention provides anumber of advantageous features including higher efficiency, lower flowrestriction, high durability (stress related or environmentally related)in the presence of abrasive particulates and a smooth outer surface freeof loose fibers or fibrils. The overall structure of the filtermaterials provides an overall thinner media allowing improved media areaper unit volume, reduced velocity through the media, improved mediaefficiency and reduced flow restrictions.

The fine fiber can be made of the polymer alloy or a polymer alloy plusadditive or other material. The polymer alloy can be formed into singlechemical specie such that it shows a single T_(g) and the DifferentialScanning calorimeter analysis reveals a single polymeric material. Sucha material, when combined with a useful additive material, can form asurface coating of the additive on the microfiber that providesoleophobicity, hydrophobicity or other associated improved stabilitywhen contacted with high temperature, high humidity and difficultoperating conditions. Such microfibers can have a smooth surfacecomprising a discrete layer of the additive material or an outer coatingof the additive material that is partly solubilized or alloyed in thepolymer surface, or both structures.

The alloy of the invention includes a polysulfone and a poly (N-vinyllactam).

Polysulfones

A polysulfone is characterized by the presence of the sulfone group in apolymer as part of its repeating unit. Whereas polysulfones may bealiphatic or aromatic, the term polysulfones in this disclosure is usedtypically to denote aromatic polysulfones having the following polymermotif:

Polysulfones are a class of amorphous thermoplastic polymerscharacterized by high glass-transition temperatures, good mechanicalstrength and stiffness, and outstanding thermal and oxidativeresistance. These polymers are characterized by the presence of thepara-linked diphenylsulfone group as part of their backbone repeatunits.

In addition to sulfone, phenyl units, and ether moieties, the mainbackbone of polysulfones can contain a number of other connecting units.The most notable such connecting group is the isopropylidene linkagethat is part of the repeat unit of the well-known bisphenol A-basedpolysulfone. In order to clearly describe the chemical makeup ofpolysulfones it is necessary to refer to the chemistry used tosynthesize them. There are several routes for the synthesis ofpolysulfones, but the one that has proved to be most practical andversatile over the years is by aromatic nucleophilic substitution. Thispolycondensation route is based on reaction of essentially equimolarquantities of 4,4′-dihalodiphenylsulfone (usuallydichlorodiphenylsulfone (DCDPS)) with a bisphenol in the presence ofbase thereby forming the aromatic ether bonds and eliminating an alkalisalt as a by-product. This route is employed almost exclusively for themanufacture of polysulfones on a commercial scale. Typical polysulfonesinclude:

Polymer Repeat Unit Structure Polysulfone Bisphenol A polysulfone

Polyethersulfone

Polyphenylsulfone

These three commercially important polysulfones referred generically bythe common names polysulfone (PST), polyethersulfone (PES), andpolyphenylsulfone (PPSF). The repeat units of these polymers are shownabove. Other polysulfones are known.

Polymerization

Commercial synthesis of poly (arylethersulfone)s is accomplished almostexclusively via the nucleophilic substitution polycondensation route.This synthesis route involves reaction of the bisphenol of choice with4,4′-dichlorodiphenylsulfone in a dipolar aprotic solvent in thepresence of an alkali base. The rate of polymerization in this type ofreaction depends on both the basicity of the bisphenol salt and theelectron-withdrawing capacity of the activating group (in this casesulfone) in the dihalide monomer.

The preferred polysulfone polymer comprises an aromatic polysulfonepolymer having the structure:

Polysulfone Bisphenol A polysulfone:

wherein the polymer has the following selected properties of preferredpolysulfone:

Solvay's UDEL 1700: Property Method Units Value Mechanical Tensilestrength at yield D 638 Psi 10,200 MPa 70 Tensile strength at yield D638 Psi 8500 MPa 59 Tensile elongation at yield D 638 % 5.7 Tensileelongation at break D 638 % 50-100 Tensile modulus D 638 kpsi 360 MPa2,480 Flexural strength D 790 psi 15,400 MPa 106 Flexural modulus D 790psi 390 MPa 2,690 Compressive strength D 695 kpsi 13.9 MPa 69Compressive modulus D 695 kpsi 374 MPa 2.58 Shear (yield) strength, D732 kpsi 6 MPa MPa 41 Notched Izod impact D 256 ft-lb/in² 1.3 J/m 69Tensile impact D 1822 ft-lb/in² 200 kJ/m² 420 Poisson ratio E 132 0.37Rockwell hardness D 785 M69 Abrasion resistance Taber 20 test usingCS-17 wheel and 1000 g load for 1000 cycles, mg/1000 cyclesMiscellaneous Color light amber Haze @ 0.10″ thickness D 1003 % 2 Lighttransmittance @ 0.10″ thickness D 1003 % 85 Refractive index 1.634Density D 792 g/cm³ 1.24 Glass-transition temperature D 3418 ° C. 185Heat deflection temperature D 648 ° C. 174 Melt Flow index. Melt flowcondition D 1238 g/ml 5.0-9.0 343° C., 2.16 Kg Coefficient of thermalexpansion D 696 ppm/° F. 31 ppm/° C. 56 Thermal conductivity E 1530Btu-in/hr-ft²-F 1.80 W/(m · K) 0.26 Water absorption, 24 hours @ 23° C.D 570 % 0.3 Mold shrinkage D 955 in/in 0.007 cm/cm 0.007

The characteristic feature of each of the polymers in the table is thehighly resonant diaryl sulfone grouping. As a consequence of the sulfuratom being in its highest state of oxidation and the enhanced resonanceof the sulfone group being in the para position, these resins offeroutstanding thermal stability and resistance to thermal oxidation. Thethermal stability is further augmented by the high bond dissociationenergies inherent in the aromatic backbone structure. As a result, thesepolymers can be melt fabricated at temperatures of up to 400° C. with noadverse consequences.

Mechanical properties of aromatic polysulfones are intimately tied tobackbone structure. For the achievement of good strength and toughnesstogether with favorable melt processing characteristics, the first andforemost requirement is a linear (unbranched) and para-linked structurefor the aryl groups in the backbone.

Aromatic polysulfones possess several common key attributes includinghigh glass-transition temperatures (generally >170° C.) and a highdegree of thermal oxidative stability. Because PSF, PES, and PPSF arefully amorphous, these resins exhibit optical transparency. Theglass-transition temperature of polysulfones produced via nucleophilicpolycondensation can be tailored by the choice of the bisphenol. Byvirtue of the chemically nonlabile aromatic ether backbone, thesepolymers exhibit superb resistance to hydrolysis in hot water and steamenvironments.

Typical Physical and Thermal Properties of PSF, PES, and PPSF PropertyPSF PES PPSF Color light light light yellow Haze As measured on 3.1-mmthick <7 <7 amber <7 amber specimens, % Light transmittance Typicalvalues; 80 70 70 varies with color. All three resins are transparent.(%) Refractive index 1.63 1.65 1.67 Density, g/cm³ 1.24 1.37 1.29Glass-transition temperature Onset 185-190 220-225 220-225 value asmeasured by differential scanning calorimetry, ° C. Heat deflectiontemperature As 167-174 195-204 207 measured on 3.1-mm thick ASTMspecimens under a load of 1.82 MPa (264 psi)., ° C. Continuous servicetemperature 160 180 180 Practical maximum long-term use temperatures forPSF and PES based on UL 746 thermal rating data; value for PPSF isestimated, ° C. Coefficient of linear thermal expansion 5.1 × 10⁻⁵ 5.5 ×10⁻⁵ 5.5 × 10⁻⁵ Specific heat at 23° C., J/(g · K) 1.00 1.12 1.17Thermal conductivity, W/(m · K) 0.26 0.18 0.35 Water absorption, in 24hours 0.22 0.61 0.37 at equilibrium 0.62 2.1 1.1 Mold shrinkage, cm/cm0.005 0.006 0.006 Temperature at 10% weight loss 512 547 550Thermogravimetric analysis run at heating rate of 10° C./min and 20mL/min gas (nitrogen or air) flow rate in nitrogen temperature at 10%weight loss in air 507 515 541

Typical Room Temperature Mechanical Properties of PSF, PES, and PPSFProperty PSF PES PPSF Tensile, flexural, and impact 70-71 80-83 70.0properties based on 3.1-mm thick ASTM specimens (yield) strength,MPa^(b) Tensile modulus, GPa 2.48 2.60 2.30 Elongation at yield, % 5.76.7 7.2 Elongation at break, % 75 25-75  60-120 Flexural strength, MPa106 111 91 Flexural modulus, GPa 2.69 2.90 2.40 Compressive strength,MPa 96 100 99 Compressive modulus, GPa 2.58 2.68 1.73 Shear (yield)strength, MPa 41.4 50 62 Notched Izod impact, J/m, No break 49-69 85690-700 for unnotched samples Tensile impact, kJ/M² 420 340 400 Poissonratio, at 0.5% strain 0.37 0.39 0.42 Rockwell hardness M69 M88 M86Abrasion resistance Taber test using 20 19 20 CS-17 wheel and 1000 gload for 1000 cycles, mg/1000 cyclesFurthermore, they can withstand acidic and alkali media over a widerange of concentrations and temperatures.

Polysulfones are rigid and tough, with practical engineering strengthand stiffness properties even without reinforcement. Their strength andstiffness at room temperature are high compared to traditional aliphaticbackbone amorphous plastics. The polymers exhibit ductile yielding overa wide range of temperatures and deformation rates. The room temperaturemechanical properties of bisphenol A, bisphenol S, and bisphenol-basedpolysulfones are shown above. The tensile and flexural properties aswell as resistance to cracking in chemical environments can besubstantially enhanced by the addition of fibrous reinforcements such aschopped glass fiber.

Polysulfones exhibit excellent inherent burning resistancecharacteristics compared to many engineering thermoplastics. The whollyaromatic polysulfones such as PES and PPSF possess particularlyoutstanding flame retardancy and very low smoke release characteristics.

Polysulfones offer excellent electrical insulative capabilities. Theresins exhibit low dielectric constants and dissipation factors even inthe GH_(z) (microwave) frequency range. This performance is retainedover a wide temperature range and has permitted many applications.

Blends and Alloys

We have surprisingly found that the polysulfone polymers can be alloyedwith an N-vinyl lactam polymer.

The blending of the polysulfone and poly (N-vinyl lactam) polymers isused to tailor existing commercial polymers to specific end userequirements. The blending of polysulfones with polymers presentsopportunities, but at the same time poses some significant technicalchallenges. Miscibility of PSF or PES with any nonsulfone-based polymeris extremely rare. Blends comprising PSF, PES, and PPSF and poly(N-vinyl lactam) are miscible, although their blends form mechanicallycompatible mixtures with relatively stable phase morphologies.

N-Vinyl Amide Polymers

N-Vinyl amide-based polymers, especially the N-vinyl lactams, such aspoly(N-vinyl-2-pyrrolidinone) or simply polyvinyl pyrrolidone (PVP)contain at least some of the following monomer residue,

and continue to be of major importance. Because of hydrogen bonding ofwater to the amide group, many of the N-vinylamide homopolymers arewater soluble or dispersible. PVP is soluble in polar solvents likealcohol. The chemistry of PVP, the most commercially successful polymerof the class, in addition to the ability to complex, PVP and itsanalogues along with a large assortment of copolymers are excellent filmformers. They exhibit the ability to interact with a variety of surfacesby hydrogen or electrostatic bonding, resulting I protective coatingsand adhesive applications of commercial significance such as hair sprayfixtures, tablet binders, disintegrants, idophors, antidye redepositionagents in detergents, protective colloids, dispersants, andsolubilizers, among many others.

N-Vinyl amides and N-vinylimides can be prepared by reaction of amidesand imides with acetylene, by dehydration of hydroxyethyl derivatives,by pyrolysis of ethylidenebisamides, or by vinyl exchange, among othermethods; the monomers are stable when properly stored. OnlyN-vinyl-2-pyrrolidinone (VP):

is of significant commercial importance in polymerization.Vinylcaprolactam is available and is growing in importance, and vinylformamide is available as a developmental monomer. The polymerscontaining VP, when alloyed with a polysulfone, obtain increased watercompatibility without loss of other valuable filtration properties.

Commonly called vinylpyrrolidinone or VP, N-vinyl-2-pyrrolidinone is aclear, colorless liquid that is miscible in all proportions with waterand most organic solvents. It can polymerize slowly by itself but can beeasily inhibited by small amounts of ammonia, sodium hydroxide (causticpellets), or antioxidants such as N,N′-di-sec-butyl-p-phenylenediamine.

The lower molecular weight grades (K-15 and K-30) of PVP are preparedindustrially with an ammonia/H₂O₂ initiation system. Such products arethe standards for the pharmaceutical industry and conform to the variousnational pharmacopeias. The H₂O₂/ammonia initiation system is notemployed commercially in the manufacture of higher molecular weighthomologues; they are prepared with organic initiators. Suchpolymerizations follow simple chain theory and are usually performed inwater commercially, the rate of polymerization is at a maximum inaqueous media at pH 8-10 and at 75 wt % monomer. Polymerization ratesfollow the polarity and hydrogen bonding capability of the solvent.

Poly(N-vinyl-2-pyrrolidinone) (PVP) is undoubtedly thebest-characterized and most widely studied N-vinyl lactam polymer.Commercial success of the material arises from its biologicalcompatibility, low toxicity, film-forming and adhesive characteristics,unusual complexing ability, relatively inert behavior toward salts andacids, and thermal and hydrolytic stability.

Poly(N-vinyl-2-pyrrolidinone) is linear N-vinyl-2-pyrrolidinone groupsof varying degrees of polymerization. The molecular weights of PVPsamples are determined by size exclusion chromatography (sec),osmometry, ultracentrifugation, light-scattering, and solution viscositytechniques. The most frequently employed method of determining andreporting the molecular weight of PVP samples utilizes the sec/low anglelight scattering (lalls) technique.

Specifications of PVP Grades Assay Value (max) K value/M_(w)10-15/600-15,000 Variation     85-115% 30-120/400,000-3,000,000Variation     90-107% Tg, ° C. 130-176 Moisture, % 5 pH, of a 5%solution in distilled water 3.0-7.0 Residue on ignition, % 0.02Aldehydes, % (as acetaldehyde) 0.02 N-vinyl-2-pyrrolidinone, monomer wt% 0.20 Lead, ppm 10 Arsenic, ppm 1 Nitrogen, % 11.5-12.8

The T_(g) of PVP is sensitive to residual moisture and unreactedmonomer. It is even sensitive to how the polymer was prepared,suggesting that MWD, branching, and crosslinking may play a part.Polymers presumably with the same molecular weight prepared by bulkpolymerization exhibit lower T_(g)s compared to samples prepared byaqueous solution polymerization, lending credence to an example ofbranching caused by chain-transfer to monomer.

One of PVP's more outstanding attributes is its solubility in both waterand a variety of organic solvents. PVP is soluble in alcohols, acids,ethyl lactate, chlorinated hydrocarbons, amines, glycols, lactams, andnitroparaffins. PVP is insoluble in hydrocarbons, ethers, ethyl acetate,sec-butyl-4-acetate, 2-butanone, acetone, cyclohexanone, andchlorobenzene.

Copolymerization

Copolymerization of N-vinyl monomers with other vinyl monomers can beachieved. Such polymerizations can be conveniently carried out inaqueous solution or in a variety of solvents, depending onmonomer/polymer solubilities. Various strategies have been employed tocompensate for the divergence in reactivity ratios in order to formuniform (statistical) copolymers such as semibatch or mixed monomerfeeds. The first commercially successful class of VP copolymers,poly(vinylpyrrolidinone-co-vinyl acetate) is currently manufactured insizeable quantities. A wide variety of compositions and molecularweights are available as powders or as solutions in ethanol,isopropanol, or water (if soluble). Desirable properties superior to PVPhomopolymer can be specified by judicious selection of the amount ofvinyl acetate. Copolymers based on DMAEMA (dimethylaminoethylmethacrylate) in either free amine form or quaternized with diethylsulfate or methyl chloride have achieved commercial significance. Themost successful of these products contain high ratios of VP to DMAEMAand are partially quaternized with diethyl sulfate (Polyquaternium 11).They afford very hard, clear, non-flaking films that are easily removedif needed. More recently, copolymers with methylvinyllimidazoliumchloride (Polyquatemium 16) or MAPTAC (methacrylamidoproppyltrimethylammonium chloride) (Polyquaternium 28) have been introduced,Unquaternized DMAEMA copolymers afford resins that are mildly cationicand less hydroscopic.

PVP/acrylic acid copolymer in powdered form prepared by precipitationpolymerization from heptane has been introduced commercially. A widevariety of compositions and molecular weights are available, from 75/25to 25/75 wt % VP/AA and from 20×10³ to 250×10³ molecular weights. Thecopolymers are insoluble in water unless they are neutralized to someextent with base. They are soluble, however, in various ratios ofalcohol and water, suggesting applications where delivery fromhydroalcoholic solutions but subsequent insolubility in water isdesired, such as in low volatile organic compound (VOC) hair-fixativeformulations or tablet coatings. Unneutralized, the T_(g) is higher thanexpected, indicating interchain hydrogen bonding.

The preferred N-vinyl lactam polymer comprises a homopolymer ofpolyvinyl pyrrolidone. The following table exhibits the preferredpolymer characteristics.

Property PVP K-30 PVP K-90 Appearance @ 25° C. Off-white, amorphousOff-white, powder amorphous powder Refractive index 1.53 1.53 K-Value26-35  90-100 (Viscosity of 1% solution) Color (APHA) 80 max.^(a) 60max.^(a) % Residual VP <0.1 <0.1 % Active 95 min. 95 min. Moisture 5max. 5 max. % Ash (combustion) 0.02 max. <0.1 pH (solids as 5%; sol'ns,3-7 3-7 as is) M_(w) Range 40,000-80,000   900,000-1,700,000 BrookfieldViscosity, cP 3 150 Film Density (g/cc) 1.207 1.216 Tg (° C.) 163 174

We have found that the alloy can be made either by solvent processing ormelt processing the polymer materials. In solvent processing, usefulamounts of the polymer are combined in solution. Useful solvents includealiphatic polar noncyclic solvents such as halogenated alkanes such aschloroform, 1,2 dichloroethane, and the like, amides, such as N,N-dimethylformamide and N, N dimethylacetamide, or other solvents suchas epicholorhydrin and diglyme. Non-aromatic polar cyclic solvent suchas ethers, including tetrahydrofuran and dioxane, pyrrolodones, such as2-methyl pyrrolodone, ketones such as cyclohexanone, and lactones, suchas gamma-butyrolactone. Other useful solvents include aromatic solventssuch as mono- and di-substituted benzene, including chlorobenzene,o-dichlorobenzene, phenol, o-chlorophenol and the like. Aromaticsolvents also include pyridine, aniline and nitrobenzene.

Mixtures of the solvents above and mixtures of these solvents withsuitable cosolvents can also be useful solvents. Cosolvents includealiphatic ketones, such as acetone and methyl ethyl ketone, ethers,esters, etc. These solutions can contain an inorganic salt that issubstantially or strongly differentiated in aqueous solution. The salthelps to control fiber size. Addition of small amounts of salts canincrease the solution conductivity. In turn, this can promote decreasein fiber diameter, disappearance of beads in the fibers, reduce spreadof fiber diameter and improve the overall uniformity in the fibrous mat.This effect, which is not fully understood, appears to be very similaracross a large number of solvent spinning systems. In our case theaddition of an alkali metal halide salt, including NaCl, KCl, LiCl andothers aims to achieve these traits, as they translate into tighterdistribution of fiber diameter and pore size.

The resulting solution of polysulfone, N-vinyl lactam polymer andsolvent is agitated until uniform and the solution obtains increasedclarity. The solution of polymers can then be processed into fiber filmor other useful structure by spinning the fiber or forming a polymerfilm while evaporating the solvent.

The alloy materials of the invention can also be made by meltprocessing. Useful amounts of the polysulfone and the N-vinyl lactammaterial are combined typically in powder, chipped or pellet form andintroduced into a melt processing unit such as an extruder, and formedinto an extrudate chip, pellet or linear member comprising the alloy.

We have found that additive materials can significantly improve theproperties of the polymer materials in the form of a fine fiber. Theresistance to the effects of heat, humidity, impact, mechanical stressand other negative environmental effect can be substantially improved bythe presence of additive materials. We have found that while processingthe microfiber materials of the invention, that the additive materialscan improve the oleophobic character, the hydrophobic character and canappear to aid in improving the chemical stability of the materials. Webelieve that the fine fibers of the invention in the form of amicrofiber are improved by the presence of these oleophobic andhydrophobic additives as these additives form a protective layercoating, ablative surface or penetrate the surface to some depth toimprove the nature of the polymeric material. We believe the importantcharacteristics of these materials are the presence of a stronglyhydrophobic group that can preferably also have oleophobic character.Strongly hydrophobic groups include fluorocarbon groups, hydrophobichydrocarbon surfactants or blocks and substantially hydrocarbonoligomeric compositions. These materials are manufactured incompositions that have a portion of the molecule that tends to becompatible with the polymer material affording typically a physical bondor association with the polymer while the strongly hydrophobic oroleophobic group, as a result of the association of the additive withthe polymer, forms a protective surface layer that resides on thesurface or becomes alloyed with or mixed with the polymer surfacelayers. The additive can be used at an amount of 1% to 25% by weighttotal on fiber. For 0.2-micron fiber with 10% additive level, thesurface thickness is calculated to be around 50 Å, if the additive hasmigrated toward the surface. Migration is believed to occur due to theincompatible nature of the oleophobic or hydrophobic groups in the bulkmaterial. A 50 Å thickness appears to be reasonable thickness forprotective coating. For 0.05-micron diameter fiber, 50 Å thicknesscorresponds to 20% mass. For 2 microns thickness fiber, 50 Å thicknesscorresponds to 2% mass. Preferably the additive materials are used at anamount of about 2 to 25 wt %. Useful surface thickness can range from 10Å to 150 Å.

Oligomeric additives that can be used in combination with the polymermaterials of the invention include oligomers having a molecular weightof about 500 to about 5000, preferably about 500 to about 3000 includingfluoro-chemicals, nonionic surfactants and low molecular weight resinsor oligomers.

The alloy can be made of a polymer material or a polymer plus additive.One preferred mode of the invention is a polymer blend comprising afirst polymer and a second, but different polymer (differing in polymertype, molecular weight or physical property) that is conditioned ortreated at elevated temperature. The polymer blend can be reacted andformed into a single chemical specie or can be physically combined intoa blended composition by an annealing process. Annealing implies aphysical change, like crystallinity, stress relaxation or orientation.Preferred materials are chemically reacted into a single polymericspecie such that a Differential Scanning calorimeter analysis reveals asingle polymeric material. Such a material, when combined with apreferred additive material, can form a surface coating of the additiveon the microfiber that provides oleophobicity, hydrophobicity or otherassociated improved stability when contacted with high temperature, highhumidity and difficult operating conditions. The fine fiber of the classof materials can have a diameter of about 0.01 to 5 microns. Suchmicrofibers can have a smooth surface comprising a discrete layer of theadditive material or an outer coating of the additive material that ispartly solubilized or alloyed in the polymer surface, or both.

The material is heated until the materials are in melt form, thematerials are intimately mixed and extruded into a pellet, linearmember, or shaped article such as film or other shaped extrudate. Theelectrostatic spinning process as disclosed in Barris et al., U.S. Pat.No. 4,650,516, can be used to form the microfiber or nanofiber of theunit. A suitable apparatus for forming the fiber is illustrated therein.This apparatus includes a reservoir in which the fine fiber formingpolymer solution is contained, a pump and a rotary type emitting deviceor emitter to which the polymeric solution is pumped. The emittergenerally consists of a rotating union, a rotating portion including aplurality of offset holes and a shaft connecting the forward facingportion and the rotating union. The rotating union provides forintroduction of the polymer solution to the forward facing portionthrough the hollow shaft. The holes are spaced around the periphery ofthe forward facing portion. Alternatively, the rotating portion can beimmersed into a reservoir of polymer fed by reservoir 80 and pump 81.Syringe needle spinning can also be used. The rotating portion thenobtains polymer solution from the reservoir and as it rotates in theelectrostatic field. A droplet of the solution forms fiber as it isaccelerated by the electrostatic field toward the collecting media asdiscussed below.

Facing the emitter, but spaced apart therefrom, is a substantiallyplanar grid upon which the collecting media (i.e. a suitable filtrationsubstrate or combined filtration substrate) is positioned. Air can bedrawn through the grid. The collecting media is passed around rollerspositioned adjacent opposite ends of grid. A high voltage electrostaticpotential is maintained between emitter and grid by means of a suitableelectrostatic voltage source or power supply connected to the grid andemitter.

In use, the polymer solution is pumped to the rotating union orreservoir from reservoir. The forward facing portion rotates whileliquid exits from holes, or is picked up from a reservoir, and movesfrom the outer edge of the emitter toward collecting media positioned ongrid. Specifically, the electrostatic potential between grid and theemitter imparts a charge to the material that cause liquid to be emittedtherefrom as thin fibers which are drawn toward grid where they arriveand are collected on substrate or an efficiency layer. In the case ofthe polymer in solution, solvent is evaporated from the fibers duringtheir flight to the collection media; therefore, the fibers arrive atand coat the substrate or efficiency layer. The fine fibers bond to thesubstrate fibers first encountered at the grid. Electrostatic fieldstrength is selected to ensure that the polymer material is acceleratedfrom the emitter to the collecting media; the acceleration is sufficientto render the material into a very thin microfiber or nanofiberstructure. Increasing or slowing the advance rate of the collectingmedia can deposit more or less emitted fibers on the forming media,thereby allowing control of the thickness of each layer depositedthereon. Alternatively, the melt polymer can be melt blown intonanofiber, microfiber or other fine fiber structures using conventionaltechnologies.

The polymer fine fiber, with a diameter of 0.01 to 10 microns,(microfiber and nanofiber) can be fashioned into useful product formats(e.g., when formed onto a substrate). Useful product formats can also beachieved by depositing multiple layers of fine fibers in order toconstruct a stand-alone nanofiber film with sufficient mechanicalstrength. One fiber size useful in high efficiency filter ranges fromabout 0.05 to 0.2 micron. This fine fiber can be made in the form of animproved multi-layer microfiltration media structure. The fine fiberlayers of the invention comprise a random distribution of fine fibersthat can be bonded to form an interlocking net. The thickness of thetypical fine fiber filtration layer ranges from about 1 to 100 times thefiber diameter with a basis weight ranging from about 0.01 to 240micrograms-cm⁻².

Filtration performance is obtained largely as a result of the fine fiberbarrier to the passage of particulate. Structural properties ofstiffness, strength, pleatability are provided by the substrate to whichthe fine fiber adhered, and/or the fine fiber multiple layeredstructure. The fine fiber interlocking networks have as importantcharacteristics, fine fibers in the form of microfibers or nanofibersand relatively small openings, orifices or spaces between the fibers.Such spaces typically range, between fibers, of about 0.01 to about 25microns or often about 0.1 to about 10 microns.

The filter products comprise a fine fiber layer formed on a substrate.Fibers from synthetic, natural sources (e.g., polyester and celluloselayers) are thin, appropriate substrate choices. In service, the filterscan stop incident particulate from passing through the fine fiber layerand can attain substantial surface loadings of trapped particles. Theparticles comprising dust or other incident particulates rapidly form adust cake on the fine fiber surface and maintain high initial andoverall efficiency of particulate removal. Even with relatively finecontaminants having a particle size of about 0.01 to about 1 micron, thefilter media comprising the fine fiber has a very high dust capacity.

The polymer materials as disclosed herein have substantially improvedresistance to the undesirable effects of heat, humidity, high flowrates, reverse pulse cleaning, operational abrasion, submicronparticulates, cleaning of filters in use and other demanding conditions.The improved microfiber and nanofiber performance is a result of theimproved character of the polymeric materials forming the microfiber ornanofiber. Further, the filter media of the invention using the improvedpolymeric materials of the invention provides a number of advantageousfeatures including higher efficiency, lower flow restriction, highdurability (stress related or environmentally related) in the presenceof abrasive particulates and a smooth outer surface free of loose fibersor fibrils. The overall structure of the filter materials provides anoverall thinner media allowing improved media area per unit volume,reduced velocity through the media, improved media efficiency andreduced flow restrictions.

A general understanding of some of the basic principles and problems ofgas, air and liquid filter design can be understood by consideration ofthe following types of filter media: surface loading media; and, depthmedia. Each of these types of media has been well studied, and each hasbeen widely utilized. Certain principles relating to them are described,for example, in Kahlbaugh et al., U.S. Pat. No. 5,082,476; Kahlbaugh etal., U.S. Pat. No. 5,238,474; and Kahlbaugh et al., U.S. Pat. No.5,364,456. The complete disclosures of these three patents areincorporated herein by reference.

Fluid streams such as air and gas streams often carry particulatematerial therein. The removal of some or all of the particulate materialfrom the fluid stream is needed. For example, air intake streams to thecabins of motorized vehicles, air in computer disk drives, HVAC air,clean room ventilation and applications using filter bags, barrierfabrics, woven materials, air to engines for motorized vehicles, or topower generation equipment; gas streams directed to gas turbines; and,air streams to various combustion furnaces, often include particulatematerial therein. In the case of cabin air filters it is desirable toremove the particulate matter for comfort of the passengers and/or foraesthetics. With respect to air and gas intake streams to engines, gasturbines and combustion furnaces, it is desirable to remove theparticulate material because particulate can cause substantial damage tothe internal workings to the various mechanisms involved. In otherinstances, production gases or off gases from industrial processes orengines may contain particulate material therein. Before such gases canbe, or should be, discharged through various downstream equipment to theatmosphere, it may be desirable to obtain a substantial removal ofparticulate material from those streams.

Paper filter elements are widely used forms of surface loading media. Ingeneral, paper elements comprise dense mats of cellulose, synthetic orother fibers oriented across a gas stream carrying particulate material.The paper is generally constructed to be permeable to the gas flow, andto also have a sufficiently fine pore size and appropriate porosity toinhibit the passage of particles greater than a selected sizetherethrough. As the gases (fluids) pass through the filter paper, theupstream side of the filter paper operates through diffusion andinterception to capture and retain selected sized particles from the gas(fluid) stream. The particles are collected as a dust cake on theupstream side of the filter paper. In time, the dust cake also begins tooperate as a filter, increasing efficiency. This is sometimes referredto as “seasoning,” i.e. development of an efficiency greater thaninitial efficiency.

A simple filter design such as that described above is subject to atleast two types of problems. First, a relatively simple flaw, i.e.rupture of the paper, results in failure of the system. Secondly,particulate material rapidly builds up on the upstream side of thefilter, as a thin dust cake or layer, increasing the pressure drop.Various methods have been applied to increase the “lifetime” ofsurface-loaded filter systems, such as paper filters. One method is toprovide the media in a pleated construction, so that the surface area ofmedia encountered by the gas flow stream is increased relative to aflat, non-pleated construction. While this increases filter lifetime, itis still substantially limited. For this reason, surface loaded mediahas primarily found use in applications wherein relatively lowvelocities through the filter media are involved, generally not higherthan about 20-30 feet per minute and typically on the order of about 10feet per minute or less. The term “velocity” in this context is theaverage velocity through the media (i.e. flow volume per media area).

In general, as air flow velocity is increased through a pleated papermedia, filter life is decreased by a factor proportional to the squareof the velocity. Thus, when a pleated paper, surface loaded, filtersystem is used as a particulate filter for a system that requiressubstantial flows of air, a relatively large surface area for the filtermedia is needed. For example, a typical cylindrical pleated paper filterelement of an over-the-highway diesel truck will be about 9-15 inches indiameter and about 12-24 inches long, with pleats about 1-2 inches deep.Thus, the filtering surface area of media (one side) is typically 30 to300 square feet.

In many applications, especially those involving relatively high flowrates, an alternative type of filter media, sometimes generally referredto as “depth” media, is used. A typical depth media comprises arelatively thick tangle of fibrous material. Depth media is generallydefined in terms of its porosity, density or percent solids content. Forexample, a 2-3% solidity media would be a depth media mat of fibersarranged such that approximately 2-3% of the overall volume comprisesfibrous materials (solids), the remainder being air or gas space.

Another useful parameter for defining depth media is fiber diameter. Ifpercent solidity is held constant, but fiber diameter (size) is reduced,pore size or interfiber space is reduced; i.e. the filter becomes moreefficient and will more effectively trap smaller particles.

A typical conventional depth media filter is a deep, relatively constant(or uniform) density, media, i.e. a system in which the solidity of thedepth media remains substantially constant throughout its thickness. By“substantially constant” in this context, it is meant that onlyrelatively minor fluctuations in density, if any, are found throughoutthe depth of the media. Such fluctuations, for example, may result froma slight compression of an outer engaged surface, by a container inwhich the filter media is positioned.

Gradient density depth media arrangements have been developed. some sucharrangements are described, for example, in Kahlbaugh et al., U.S. Pat.No. 5,082,476; Kahlbaugh et al., U.S. Pat. No. 5,238,474; and Kahlbaughet al., U.S. Pat. No. 5,364,456. In general, a depth media arrangementcan be designed to provide “loading” of particulate materialssubstantially throughout its volume or depth. Thus, such arrangementscan be designed to load with a higher amount of particulate material,relative to surface loaded systems, when full filter lifetime isreached. However, in general the tradeoff for such arrangements has beenefficiency, since, for substantial loading, a relatively low soliditymedia is desired. Gradient density systems such as those in the patentsreferred to above, have been designed to provide for substantialefficiency and longer life. In some instances, surface-loading media isutilized as a “polish” filter in such arrangements.

A filter media construction according to the present invention includesa first layer of permeable coarse fibrous media or substrate having afirst surface. A first layer of fine fiber media is secured to the firstsurface of the first layer of permeable coarse fibrous media. Preferablythe first layer of permeable coarse fibrous material comprises fibershaving an average diameter of at least 10 microns, typically andpreferably about 12 (or 14) to 30 microns. Also preferably the firstlayer of permeable coarse fibrous material comprises a media having abasis weight of no greater than about 200 grams/meter², preferably about0.50 to 150 g/m², and most preferably at least 8 g/m². Preferably thefirst layer of permeable coarse fibrous media is at least 0.0005 inch(12 microns) thick, and typically 0.0006 to 0.02 (15 to 500 microns)thick and preferably is about 0.001 to 0.030 inch (25-800 microns)thick.

In preferred arrangements, the first layer of permeable coarse fibrousmaterial comprises a material which, if evaluated separately from aremainder of the construction by the Frazier permeability test, wouldexhibit a permeability of at least 1 meter(s)/min, and typically andpreferably about 2-900 meters/min. Herein when reference is made toefficiency, unless otherwise specified, reference is meant to efficiencywhen measured according to ASTM-1215-89, with 0.78μ monodispersepolystyrene spherical particles, at 20 fpm (6.1 meters/min) as describedherein.

Preferably the layer of fine fiber material secured to the first surfaceof the layer of permeable coarse fibrous media is a layer of nano- andmicrofiber media wherein the fibers have average fiber diameters of nogreater than about 2 to 10 microns, generally and preferably no greaterthan about 5 microns, and typically and preferably have at least somefiber with diameters smaller than 0.5 micron and within the range ofabout 0.05 to 0.5 micron. Also, preferably the first layer of fine fibermaterial secured to the first surface of the first layer of permeablecoarse fibrous material has an overall thickness that is no greater thanabout 50 microns or in certain applications about 30 microns, morepreferably no more than 20 microns, most preferably no greater thanabout 10 microns, and typically and preferably that is within athickness of about 1-8 times (and more preferably no more than 5 times)the fine fiber average diameter of the layer.

Certain preferred arrangements according to the present inventioninclude filter media as generally defined, in an overall filterconstruction. Some preferred arrangements for such use comprise themedia arranged in a cylindrical, pleated configuration with the pleatsextending generally longitudinally, i.e. in the same direction as alongitudinal axis of the cylindrical pattern. For such arrangements, themedia may be imbedded in end caps, as with conventional filters. Sucharrangements may include upstream liners and downstream liners ifdesired, for typical conventional purposes.

In some applications, media according to the present invention may beused in conjunction with other types of media, for example conventionalmedia, to improve overall filtering performance or lifetime. Forexample, media according to the present invention may be laminated toconventional media, be utilized in stack arrangements; or beincorporated (an integral feature) into media structures including oneor more regions of conventional media. It may be used upstream of suchmedia, for good load; and/or, it may be used downstream fromconventional media, as a high efficiency polishing filter.

Certain arrangements according to the present invention may also beutilized in liquid filter systems, i.e. wherein the particulate materialto be filtered is carried in a liquid. Also, certain arrangementsaccording to the present invention may be used in mist collectors, forexample arrangements for filtering fine mists from air.

According to the present invention, methods are provided for filtering.The methods generally involve utilization of media as described toadvantage, for filtering. As will be seen from the descriptions andexamples below, media according to the present invention can bespecifically configured and constructed to provide relatively long lifein relatively efficient systems, to advantage.

Various filter designs are shown in patents disclosing and claimingvarious aspects of filter structure and structures used with the filtermaterials. Engel et al., U.S. Pat. No. 4,720,292, disclose a radial sealdesign for a filter assembly having a generally cylindrical filterelement design, the filter element being sealed by a relatively soft,rubber-like end cap having a cylindrical, radially inwardly facingsurface. Kahlbaugh et al., U.S. Pat. No. 5,082,476, disclose a filterdesign using a depth media comprising a foam substrate with pleatedcomponents combined with the microfiber materials of the invention.Stifelman et al., U.S. Pat. No. 5,104,537, relate to a filter structureuseful for filtering liquid media. Liquid is entrained into the filterhousing, passes through the exterior of the filter into an interiorannular core and then returns to active use in the structure. Suchfilters are highly useful for filtering hydraulic fluids. Engel et al.,U.S. Pat. No. 5,613,992, show a typical diesel engine air intake filterstructure. The structure obtains air from the external aspect of thehousing that may or may not contain entrained moisture. The air passesthrough the filter while the moisture can pass to the bottom of thehousing and can drain from the housing. Gillingham et al., U.S. Pat. No.5,820,646, disclose a Z filter structure that uses a specific pleatedfilter design involving plugged passages that require a fluid stream topass through at least one layer of filter media in a “Z” shaped path toobtain proper filtering performance. The filter media formed into thepleated Z shaped format can contain the fine fiber media of theinvention. Glen et al., U.S. Pat. No. 5,853,442, disclose a bag housestructure having filter elements that can contain the fine fiberstructures of the invention. Berkhoel et al., U.S. Pat. No. 5,954,849,show a dust collector structure useful in processing typically airhaving large dust loads to filter dust from an air stream afterprocessing a workpiece generates a significant dust load in anenvironmental air. Lastly, Gillingham, U.S. Design Pat. No. 425,189,discloses a panel filter using the Z filter design.

EXPERIMENTAL Example 1

A polymer solution was obtained by combining polymer and solvent in a500 ml glass kettle with 3-neck lid, to which mechanical stirring, atemperature probe, and a condenser were attached. The vessel placed in aheating mantle and the temperature controlled at 60° C. under withconstant agitation until a uniform solution was obtained. The solutionwas cooled at room temperature before electrospinning.

Solution composition: 20% solids, with a composition of 100%polysulfone, UDEL 1700 (from Solvey), polymer by weight and a solventcomposition of 50% THF and 50% DMF by weight.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.1ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 25 Kvolts.

Example 2

A polymer solution was obtained as in Example 1 by combining polymer andsolvent in a container with constant agitation until a uniform solutionwas obtained.

Solution composition: 30% solids, with a composition of 100% PVP,Luvitec K30 (from BASF), by weight and a solvent composition of 34% THFand 66% DMF by weight.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.1ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 17 Kvolts.

Example 3

A polymer solution was obtained as in Example 1 by combining thepolymers and solvent in a container with constant agitation until auniform solution was obtained.

Solution composition: 20% solids, with a composition of polysulfone 50%,UDEL 1700 (from Solvey), and 50% PVP, Luvitec K30 (from BASF), byweight, in solutions of a solvent composition of 50% THF and 50% DMF byweight.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.1ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 17 Kvolts. FIGS. 4and 5 are SEM photo micrographs of the fiber of Example 3.

Differential Scanning Calorimetry Analysis

The samples were analyzed using a TA Instruments Differential Scanningcalorimeter. (DSC). The samples were weighed and crimped in an aluminumpan and run for 3 cycles (second cycle shown) from 30° C. equilibrationto 250° C. The samples were ramped at 10° C. per minute under a nitrogenatmosphere. FIG. 1 shows the DSC curves for the polysulfone/PVP alloyfibers (Example 3) and for fibers of individual polymer species(Examples 1 and 2).

Example 4

A polymer solution was obtained as in Example 1 by combining thepolymers and solvent in a container with constant agitation until auniform solution was obtained.

Solution composition: 20% solids, with a composition polysulfone 75%,UDEL 1700 (from Solvey), by weight and 25% PVP, Luvitec K30 (from BASF)in solutions of a solvent composition of 50% THF and 50% DMF by weight.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.1ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 20 Kvolts.Differential Scanning calorimetry Analysis as in Example 1. FIG. 2 showsthe DSC curves for the polysulfone/PVP alloy fibers (Example 4) and forfibers of individual polymer species (Examples 1 and 2). FIG. 9 is a SEMphoto micrograph of the fiber of Example 4.

Example 5

A polymer solution was obtained as in Example 1 by combining thepolymers and solvent in a container with constant agitation until auniform solution was obtained. Solution composition: 20% solids, with acomposition of 25% polysulfone, UDEL 1700 (from Solvey), and 75% PVP,Luvitec K30 (from BASF) by weight, in solutions of a solvent compositionof 50% THF and 50% DMF by weight.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.1ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 18 Kvolts.Differential Scanning calorimetry Analysis as in Example 1. FIG. 3 showsthe DSC curves for the polysulfone/PVP alloy fibers (Example 5) and forfibers of individual polymer species (Examples 1 and 2). FIG. 17 is aSEM photo micrograph of the fiber of Example 5.

Example 6

A polymer solution was obtained as in Example 1 by combining thepolymers and solvent in a container with constant agitation until auniform solution was obtained. Solution composition: 15% solids, with acomposition of polysulfone 50%, UDEL 1700 (from Solvey), by weight and50% PVP, Luvitec K30 30 (from BASF), in solutions of a solventcomposition of 50% THF and 50% DMF by weight. LiCl was added to thesolution to result in a 0.04% overall salt concentration.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.05ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 15 Kvolts. FIG. 13 isa SEM photo micrograph of the fiber of Example 6.

Example 7

A polymer solution was obtained as in Example 1 by combining thepolymers and solvent in a container with constant agitation until auniform solution was obtained. Solution composition: 22% solids, with acomposition polysulfone, UDEL 1700 (from Solvey), 90% by weight and 10%PVP, Luvitech K30 (from BASF) in a solution of a solvent composition of40% THF and 60% DMF by weight.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.1ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 15 Kvolts.

Example 8

Using the solution and electrospinning conditions of Example 3, filtercomposite structures were fabricated by electrospinning onto a standardpolyester non-woven media, rotating on a metal drum. The resulting fibermat had an average fiber diameter of 1.2 μm, with an overall thicknessof 8 μm, and an estimated deposited amount of 3.5 g/m².

Example 9

Using the following conditions, filter composite structures werefabricated by electrospinning onto a standard polyester non-woven media,rotating on a metal drum. Solution composition: 17.5% solids, with acomposition polysulfone 50%, UDEL 1700 (from Solvey), by weight and 50%PVP, Luvitec K30 (from BASF), in solutions of a solvent composition of50% THF and 50% DMF by weight. LiCl was added to the solution to resultin a 0.04% overall salt concentration.

Electrospinning conditions: Solution electrospun onto aluminum substratevia a syringe, which flow is controlled through a syringe pump at 0.05ml/min. The distance between the tip (needle) of the syringe and thealuminum substrate at 6 inches. Applied voltage of 15 Kvolts. 35%relative humidity. The resulting fiber mat had an average fiber diameterof 0.4 μm, with an overall thickness of 4 μm, and an estimated depositedamount of 1.5 g/m².

Example 10

Same conditions as Example 9, with longer fiber deposition time toresult in a nanofiber mat thicker nanofiber mat. The resulting fiber mathad an average fiber diameter of 0.4 μm, with an overall thickness of 8μm, and an estimated deposited amount of 3.5 g/m².

Water Resistance In order to verify the resistance of the fibers to hotwater environment, selected samples were immersed in boiling water for24 hours. In addition to “as made samples”, samples annealed at 200° C.for 10 minutes were also included. SEM micrographs were taken before andafter each treatment in order to evaluate morphological changes thatcould have occurred. FIG. 6 shows a SEM photo micrograph of the fiber ofExample 3 immersed in boiling water for 24 hours.

FIG. 7 shows a SEM photo micrograph of the fiber of Example 3 afterannealing at 190° C. for 10 min. FIG. 8 shows a SEM photo micrograph ofthe fiber of Example 3 after annealing at 190° C. for 10 min, and afterbeing immersed in boiling water for 24 hours.

FIG. 10 shows a SEM photo micrograph of the fiber of Example 4 immersedin boiling water for 24 hours. FIG. 11 shows a SEM photo micrograph ofthe fiber of Example 4 after annealing at 190° C. for 10 min. FIG. 12shows a SEM photo micrograph of the fiber of Example 4 after annealingat 190° C. for 10 min. and after being immersed in boiling water for 24hours.

FIG. 14 shows a SEM photo micrograph of the fiber of Example 6 immersedin boiling water for 24 hours. FIG. 15 shows a SEM photo micrograph ofthe fiber of Example 6 after annealing at 190° C. for 10 min. FIG. 16shows a SEM photo micrograph of the fiber of Example 6 after annealingat 190° C. for 10 min. and after being immersed in boiling water for 24hours. FIG. 18 shows a SEM photo micrograph of the fiber of Example 5immersed in boiling water for 24 hours. FIG. 19 shows a SEM photomicrograph of the fiber of Example 5 after annealing at 190° C. for 10min. FIG. 20 shows a SEM photo micrograph of the fiber of Example 5after annealing at 190° C. for 10 min. and after being immersed inboiling water for 24 hours.

Hydrophilicity/Hydrophobicity. Water dynamic contact angle measurementswere employed in order to assess the relative hydrophilicity of thefiber matrices. Initial contact angle values, as well as values afterthe first few seconds can serve as qualitative measure of the matriceshydrophilicity and related wicking properties. The measurements wereperformed using the FTA 200 goniometer from First Ten Angstromsubstantially as described in the operations manual. For dynamic contactangle measurements, liquids were loaded into an application device andapplied as designed. Computer software controlled the dispensing rateand the contact angle was obtained for analysis using software providedwith the goniometer. Images were taken as designated in the operationsmanual.

FIG. 21 shows the Dynamic water contact angle for Examples 1, 4, 5 and 7unannealed and annealed. The use of the alloy of the invention obtaineda low contact angle that establishes a substantial hydrophilic nature.

Air Filtration Performance LEFS Efficiency: A 4 inch diameter sample wascut from the media. Particle capture efficiency of the test specimen iscalculated using 0.8 μm latex spheres as a test challenge contaminant inthe LEFS bench operating at 20 PPM.

Air Flow Measurements of air flow were performed on a TEXTEST FX 3300instrument operating at 125 Pa.

Efficiency Pressure drop Air Flow Sample (%) (mm H₂O) (ft³-min⁻¹ at 125Pa) Substrate Remay 2214 5 0.02 500 Example 8 45 0.03 235 Example 9 750.11 125 Example 10 77 0.13 85

Example 11

Pore Sizes, Water Flow Water flow Mean flow Nanofiber layer (ml-sec⁻¹,0.6 cm dia. pore diameter Thickness @ 3 Kpa) (μm) Substrate N/A 16.5 35Example 8 8 μm 4.5 10 Example 9 4 μm 3.5 3.0 Example 10 8 μm 3.1 2.5Pore diameter and water flow were measured using the standard procedurefor a capillary flow porometer, PMI APP 1200 AEXSC.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

1-9. (canceled)
 10. A fine fiber comprising a thermoplastic polymeralloy comprising: (a) an N-vinyl lactam polymer; and (b) a polysulfonepolymer; wherein the alloy displays a single glass transitiontemperature (T_(g)), wherein said T_(g) is found at a temperature thatranges from about 180 to about 190° C., wherein the fine fiber has afiber diameter that ranges from about 0.001 to about 5 microns.
 11. Thefiber of claim 10 wherein the fiber comprises greater than about 25 wt %of the N-vinyl lactam polymer.
 12. The fiber of claim 10 wherein theN-vinyl lactam polymer is a vinyl pyrrolidone polymer.
 13. The fiber ofclaim 11 wherein the polysulfone is a bisphenol-A polysulfone.
 14. Thefiber of claim 10 wherein the polysulfone is a polysulfone copolymer.15. The fiber of claim 10 wherein the fiber comprises about 25 to 75 wt% of a polyvinyl pyrrolidone and about 25 to 75 wt % of thebisphenol-A-polysulfone.
 16. The fiber of claim 10 wherein the fibercomprises about 0.001 to 5 wt % of an inorganic metal salt.
 17. Thefiber of claim 16 wherein the salt comprises an alkali metal halide. 18.The fiber of claim 10 wherein the fine fiber has a fiber diameter thatranges from about 0.02 to about 5 microns.
 19. The fiber of claim 10wherein the fine fiber has a fiber diameter that ranges from about 0.03to about 1 microns. 20-57. (canceled)
 58. The fiber of claim 18 whereinthe fiber is in a fiber layer the layer having a thickness of about 1 to100 times the fiber diameter with a basis weight of about 0.01 to 240gm-m⁻².